The Smoking Gun of Baryon Number Violation
P. Skands
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• Baryon Number Violation (BNV) in SUSY
– Implementation of 2- and 3-body decays in the PYTHIA generator
• BNV Colour Topologies
– Baryon Number Violation and String Topologies
– An explicit detailed model baryon number flow
• Properties and predictions
• Summary and Outlook
The Smoking Gun of Baryon Number Violation
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R, B, or L? (Fast-forward)
Decent physics case + interesting to explore phenomenology
• Most general MSSM Superpotential:
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Collider Phenomenology
• General problem: how to obtain fully exclusive descriptions of collider final states (in any physics model, SM or BSM)
Non-Perturbativehadronisation, colour reconnections, beam remnants, non-perturbative fragmentation functions, pion/proton, kaon/pion, ...
Soft Jets + Jet StructureMultiple collinear/soft emissions (initial and final state brems radiation), Underlying Event (multiple perturbative 22 interactions + … ?), semi-hard separate brems jets
Resonance Masses …
Hard Jet TailHigh-pT wide-angle jets
& W
idths
+ “UNPHYSICAL” SCALES:+ “UNPHYSICAL” SCALES:
• QF , QR : Factorisation & Renormalisation
s
This has an S matrix expressible as a series in gi, ln(Q1/Q2), ln(x), m-1, fπ
-1 , …
To do precision physics:
Need to compute and/or control all large terms
EVENT GENERATORS
Inclusive
Exclusive
Hadron Decays
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Implementation of 2- and 3-body decays in PYTHIA
Partial widths: LO ME’s, (only 3rd gen massive)
Kinematics: isotropic 3-body (good when intermediate states very off shell).
Final state parton multiplicity increased by subsequent showers
NB: only MSSM pair production included (no single sparticle production)
Dreiner, Richardson, Seymour: JHEP 04(2000)008
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• Baryon Number Violation (BNV) in SUSY
– Implementation of 2- and 3-body decays in the PYTHIA generator
• BNV Colour Topologies
– Baryon Number Violation and String Topologies
– An explicit detailed model baryon number flow
• Properties and predictions
• Summary and Outlook
The Smoking Gun of Baryon Number Violation
7
Colour Topologies
Confinement potential: non-perturbative breakups hadrons
Not a priori calculable QCD-inspired phenomenological models
Semi-classical, based on colour dipoles: “Clusters” or “String pieces”
Basic problem easy to understand:
No dipole!
blue antiblue
green red
blue
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String Topologies
How does the system hadronize?
• Assume vacuum still acts as dual colour superconductor colour vortex lines ~ string picture still applicable
• Q then: which string topology? Y, Δ, V, … ?
Montanet, Rossi, Veneziano : Phys.Rep.63(1980)149
&Minimization of potential energy ~ string length (V(r) = κr)
Picture of Y-shaped topology with ‘string junction’
junction
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How does the junction act / move?
The Junction
LABBoostJRF
Inverse boost handle on motion of the baryon number, through fragmentation
T. Sjostrand, PS Nucl.Phys.B659(2003)243
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‘Ordinary strings’ same fragmentation functions, u:d:s, etc
Hadronisation
‘junction baryon’
Technically: 2 least energetic strings fragmented outwards-in
When little energy left, remains collapsed into diquark
remaining qq – q string piece fragmented as usual
Note: baryon number can be entirely separated from leading flavours
T. Sjostrand, PS Nucl.Phys.B659(2003)243
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(More Complicated Topologies)
2 possibilities:
• a) 2 junction baryons
• b) junction-junction annihilation
Select between a/b based on which topology has smallest ‘string length’ non-trivial kinematical dependence
T. Sjostrand, PS Nucl.Phys.B659(2003)243
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(More Complicated Topologies)
T. Sjostrand, PS Nucl.Phys.B659(2003)243
13
• Baryon Number Violation (BNV) in SUSY
– Implementation of 2- and 3-body decays in the PYTHIA generator
• BNV Colour Topologies
– Baryon Number Violation and String Topologies
– An explicit detailed model baryon number flow
• Properties and predictions
• Summary and Outlook
The Smoking Gun of Baryon Number Violation
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Variation of Fragmentation Assumptions
PYTHIA model: essentially stable
(provided junction Y topology ‘agreed’ upon)
Central Point Junction baryons are soft, in CM of decay
PYTHIA vs HERWIG: it matters whether B flow modeled or not
(HERWIG impl. focussed on perturbative part)
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Slow Baryons @ LHC – How tough to do?
(simplistic!)
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Slow Baryons @ LHC – How tough to do?
Not trivial. But with high cross sections (low masses) may be feasible. Would be smoking gun of Baryon Number Violation.
ILC highly interesting as well. Model applicable to any collider type.
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Summary and Outlook
• RPV-SUSY interesting phenomenology
• Esp. BNV has antisymmetric colour structure in interaction term which does not appear in SM (neglecting sphalerons …)
• Detailed model focussing on NP aspects (flow of baryon number) shows new aspects:
• Available in the PYTHIA generator (see e,g, PYTHIA 6.4 manual, published last week: JHEP05(2006)026, 582pp )
• Not trivial to ‘catch the baryon’ at LHC. Would need detailed study.
• Possibilities at ILC also remain to be explored
• Though we only applied it to BNV-SUSY, the fragmentation principles are universal, and could easily be used for other BNV physics (so far, we e.g. recycled it for proton remnant fragmentation in min-bias)
Smoking gun of BNV = excess of soft baryons (in CM of decay)
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